Rock drill bit



Dec. 9, 1958 J. s. EDGAR 2,363,686

' ROCK DRILL BIT Filed April 27, 1954 q' F-C7Z" 2371 5 *IJZUT v JohnSianiey Ed gar ROCK DRELL BIT John Stanley Edgar, Saint Catharines,Ontario, Canada, assignor to Thompson Products, Ltd, Saint Catharines,Gntario, Canada, a corporation of Ontario Application April 27, 1954,Seriai No. 425,938

2 Claims. (Cl. 287-126) The instant invention relates to an improveddrill assembly and method of producing the same, and more particularly,to an improved rock drill assembly of the type wherein the bit isdetachable from the shank and is retained thereon by an interference orpress-fit, and to an improved method of producing such an assembly.

Although the teachings of the present invention will be applicable to anumber of phases in the drilling art, the particular invention will bedescribed in detail in connection with rock drill bits and assembliescontaining the same. Such assemblies comprise a metal drill bit body,usually made of steel, having carbide inserts mounted on the drillingface thereof and having a socket on the back thereof for receiving theshank. The shank is press-fit into the socket during assembly; and afterthe drill bit has been used for a while and requires repair orrebuilding, the drill bit body is forced oif the shank, repair isneeded, and then press-fit back onto the shank. This operation may berepeated a number of times. It has been found, however, that the life ofthese parts} and particularly the drill bit body, is greatly shortenedbecause of the failure to obtain a proper fit between the bit body andthe shank after a relatively few number of removals and replacements ofthe bit body on the shank. Damage, particularly to the walls of the bitsocket, by tearing or otherwise injuring the walls, apparently duringthe press-fit assembly or disassembly, causes an improper fit betweenthe two parts and thus shortens the useful life thereof.

Although certain precautions have been taken heretofore to avoid thisdamage, these have left much to be desired. A particular difiicultyherein resides in the fact that these parts must be handled at thedrilling site, where production time is of great importance and wherethe operators are often 'not cooperative in carrying out the variousoperational steps required to avoid damage.

The instant invention resides in the provision of a protective liningfor the surfaces which are press-fit, which is substantially fool-proofin that it' avoidsthe necessity for having complete cooperation with themining operators in preventing damage to the parts. The instantinvention provides for the use of a permanent thin crystalline coherentlubricant coating which is applied to either the walls of the shank orthe walls of the socket or both, and which remains on these walls duringthe repeated assembly and disassembly steps so as to continuouslyfurnish protection therefor. It has been found that this type of coatingprovides adequate lubrication for the assembly and disassembly steps,without interfering with proper functioning of the two parts whenpress-fit together, during drilling, etc.

It is therefore an important object of the instant invention to providean improved method of preparing the same.

It is a further object of the instant invention to provide an improveddrill assembly comprising a metal drill bit body having a wall portiondefining a shank-receiving socket therein, a metal shank adapted to bepress-fit into said socket and having a wall portion for engaging thesocket wall portion, and a thin crystalline coherent lubricant coatingof a metallic salt chemically bonded to at least one of said wallportions, said bit and said shank being press-fit together; and animproved method of producing such a drill assembly which comprises thestep of coating at least one of said wall portions with a chemicalsolution which reacts with the metal to produce thereon the thincrystalline coherent lubricant coating of a metallic salt chemicallybonded thereto.

Other and further objects, features and advantages of the instantinvention will become apparent to those skilled in the art from thefollowing detailed disclosure thereof and from the drawings which form apart hereof and which describe a preferred embodiment of the instantinvention.

On the drawings:

Figure l is a full view in elevation of a drill bit assembly embodyingthe instant invention;

Figure 2 is an elevational sectional view taken substantially along theline II-II of Figure 1;

Figure 3 is an exploded view with parts shown in section and partsbroken away of the drill bit body and the shank of the instant assembly;

Figure 4 is an end view of the drill bit body, taken substantially alongthe line IV-IV of Figure 3;

Figure 5 is an enlarged fragmentary sectional view taken substantiallyalong the line V-V of Figure 3; and

Figure 6 is a fragmentary enlarged detail view taken substantially alongthe line VI-VI of'Figure 3.

As shown on the drawings:

In Figures 1 and 2, there is shown a drill bit assembly indicatedgenerally by the reference numeral 10, which comprises a metal drill bitbody 11 having a wall portion 131a defining a generally cylindrical (buttapering slightly inwardly) shank-receiving socket therein, a metalshank 12 adapted to be press-fit into the socket defined by the walls11a and having a corresponding wall portion 12a for engaging the socketwall portion 11a, and a thin crystalline coherent lubricant coating 13of a metallic salt chemically bonded to at least one of said wallportions, in this case, the socket wall portion 11a, said bit body 11and said shank l2 being press-fit together.

In the particular bit body 11 here shown, the drilling face 11b has fourgenerally rectangular grooves 11c extending radially from a centralaperture, at 14 (designated in Figure 2) and the grooves seat suitablecarbide inserts 1551,1512, 15c,and 15d therein (the inserts being shownin full view in Figure 2). The inserts 15 provide the necessary cuttingedges for effecting the drilling; and the bit body 11 isgrooved at 16a,16b, 16c and 16d, on the drilling face 11b between the inserts 15a, 15b,15c and 15d so as to provide a fluid outlet for drilling fluid whichpasses downwardly through the central aperture 14 then radiallyoutwardly through channels at 17 on the drilling face 11b and thenlongitudinally back through the axially aligned aperture 14 in the bitbody 11. The details of structure outlined in the instant paragraph aremerelyexemplary of a type of drill bit assembly which may be used in thepractice of the instant invention; and it will be appreciated thatvarious other drill bit body structures may also be used as well asvarious other shank structures, the essence of the present in- PatentedDec. 9, 1958' 3 1 vention residing in the positioning of the lining 13in the drill bit socket.

Referring to the lining 13 shown in Figure 2, it will be noted that thislining or coating 13 is applied only to the walls 11a of the drill bitbody, but it will 'be appreciated that the lining or coating may beapplied to'both the walls 11a and the walls 12a (as is shown in Figure3) or it may be applied only to the walls 12a of theshank 12. Thislatterstructure, although operative for'the purposes of the instantinvention, is less preferred, because the shanks are often made atdrilling site where the coating might be more difficult to apply,whereas the bit bodies are manufactured in a shop whereat theapplication of the coating would be less difiicult. For this reason, themost preferred embodiment of the invention is one wherein the walls 11adefining the drill bit socket have the coating 13 applied thereto, witha corresponding coating optionally applied to the shank 12.

Referring now to Figures 3, 4, and 6, it will be noted that the generalstructure of the drill bit assembly shown therein is substantiallyidentical to that shown in Figures- 1 and 2, with the single exceptionthat a coating or lining such as the coating 13 is applied to both thesocket (designated by the reference numeral 23a) and the shank (whereatit is designated by the reference numeral 23b). The reference numeralsused in Figures 3, 4, 5 and 6 in the 20 series of numbers indicate theparts or elements which are the same as those designated by thecorresponding number in the series of numbers used in Figures 1 and 2;in other words, the drill bit body 21 of Figures 3, 4, 5 and 6 is thesame as the drill bit body 11 of Figures 1 and 2, etc. It will also benoted that the coatings 13, 23a and 23b are shown without section linesfor the sake of simplicity in Figures 2, 3 and 4; and are shown insection in the enlarged views of Figures 5 and 6.

The present invention is based upon the discovery that the particularcoatings here employed possess a certain combination of properties whichinclude self-lubrication to an extent suflicient to protect the metalparts but to an extent insufficient to cause slipping between the metalparts during the drilling operation or other breakdown of theinterference fit therebetween. In addition, the instant coatings havesufficient adherence to the surface to which they are applied to permitrepeated use of the parts thus coated without breakdown of the coatinglayer. This provides the unique advantage of having the protective layeralready installed in, for example, the drill bit body 11 so thatoperators in the field are not required to take any steps at all inconnection with applying a protective coating or otherwise attempting toaccomplish this purpose. The necessity for complete cooperation betweenthe drill operators and the bit manufacturersin connection with takingthe necessary precautionary steps is eliminated.

The instant coatings are of a type known as surface conversion orchemical dip coatings, which are produced by actually converting thesurface of a metal into an oxide, salt or other chemical compound ofexceedingly low solubility in the environment to which the metal surfaceis ultimately to be exposed. In a sense, these coatings may beconsidered to be corrosion-resistant and are applied to the surface ofthe metal so as to provide a coating of the corrosion product ofthe'metal, which prevents further corrosion. In general, these surfacefilms or coatings are formed from phosphate, chromate or oxalatesolutions. The most preferred being phosphate solutions, which areapplied in the so-called Parkerizing process, and related processesinvolving improvements thereover. Some of the earlier phosphate coatingsapplied to ferrous surfaces were applied by the use of a solution ofphosphoric acid and ferrous sulfate. Zinc sulfate may be substituted forthe ferrous sulfate in applying suitable coatings. The originalParkerizing process, however, involved the use of primary imanganousphosphate in aqueous solution. The processes of this type, including theParkerizing process and the improvements made thereon are well known tothe art and the specific details thereof need not be described herein.It will be noted, however, that each of these processes, which producesa thin crystalline coherent lubricant coating of a metallic oxide orsalt on the metal surface, which crystalline coating is chemically aswell as physically bonded to the metal surface, may be used in thepractice of the instant invention. The crystals of these coatings are inheterogeneous crystalline joint with the metal base and are tightlygrown together with the latter.

At the present time, a number of commercial processes are employed forthe purpose of applying coatings, which have now been found to beunusually satisfactory for use in the instant invention. A typicalexample of a coating formulation which has been found to giveparticularly satisfactory results in the practice of the invention is asfollows:

Water 2500 Using pounds of the foregoing solution in 750 pounds ofwater, a properly diluted solution is obtained. This formulation isdisclosed in Glasson Patent No. 2,296,844, issued September 29, 1942.The instant formulation is applied by immersing the shank or the drillbit body of the instant invention in the solution for from 1 to 5minutes at temperatures within the range of l60-200 F. Other proceduresmay, of course, be employed. Such other procedures include the use ofdifferent times and temperatures, the times and temperatures beingcorrelated merely to the extent necessary to apply an appreciable amountof the instant crystalline coating. Any appreciable amount of theinstant coating, which skilled operators can readily detect, issuificient to afford the advantages of the instant invention, so theparticular details relating to the amount of coating applied are thoseoperating conditions which suit the particular skilled operator in theart. For example, in the original Parkerizing process, times of as muchas 3 to 4 hours were used, although modern methods have now improvedthis process to the extent that coating times of as little as 30 secondsmay be used. The solution may employ other dihydrogen phosphates inplace of the above recited zinc dihydrogen phosphate, such as thecorresponding salts of cadmium, calcium, strontium, barium, chromium,and manganese. A small amount of a copper salt in the bath also tends toreduce the processing time, but the alkali nitrate here used isgenerally considered superior for this purpose.

Other operative coatings may also be applied from chromic acid,dichromate or strong alkali solutions. It will also be appreciated thatthe application of these coatings is not necessarily limited to ferrousmetals, although in the drill bit art the bit body or matrix is almostinvariably made of steel.

The coatings thus produced on the metal surfaces are preferablydeposited from aqueous solutions of reagents capable of producing suchcoatings, which may be the salts of the same metal which forms thesurface of the article orsalts of a metal different from that of thearticle, or mixtures of such salts. With ferrous metals, coatings ofiron phosphates and/0r complexes thereof are preferred. Correspondingsalts of oxalic acid may also be used. The films or coatings thus formedare dense thin coherent coatings which are crystalline in characterwherein the acid has combined both chemically and physically with themetal of the base.

Processwise, the invention consists in producing a drill bit assembly 10which comprises forming a metal drill bit body 11 having a wall portion11a defining a shankreceiving socket therein, forming a metal shank 12adapted to press-fit into the socket and having a wall portion 12a forengaging the socket wall portion 11a, coating at least one of the wallportions 11a and 12a with a chemical solution (i. e., a phosphatesolution) which reacts with the (ferrous) metal to produce thereon athin crystalline coherent lubricant coating of a metal salt (i. e., aniron phosphate salt or complex) chemically bonded to the wall portion(in this case the wall 11a), and press-fitting the shank 12 into thesocket.

The instant invention has been field tested and the tests have clearlydemonstrated the superior results obtained in the practice of theinstant invention.

It will be understood that modifications and variations may be effectedwithout departing from the scope of the novel concepts of the presentinvention.

I claim as my invention:

1. A drill assembly comprising a metal drill bit body having a wallportion defining a shank-receiving socket therein, a metal shankpress-fit into said socket and having a wall portion engaging the socketwall portion, and a thin crystalline coherent lubricant coating of ametallic phosphate salt chemically bonded to at least one of said wallportions in the area of engagement therebetween.

2. A method of producing a drill assembly, that comprises providing asteel drill bit body having a Wall portion defining a shank-receivingsocket therein, providing a steel shank adapted to be press-fit intosaid socket and having a wall portion for engaging the socket wallportion, coating at least one of said wall portions with a dilutephosphate solution which reacts with the steel to produce thereon a thincrystalline coherent lubricant coating of a metallic phosphate saltchemically bonded thereto, and press-fitting said shank into saidsocket.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain Sept. 20, 1939

